Air bubble detector device

Abstract

A device is provided for detection of presence of air within a fluid system containing a dielectric fluid, such as oil. The device comprises a capacitor having a tubular capacitor plate which is connected in series with the fluid system. An elongated cylindrical capacitor plate is coaxially secured within the tube by disc shaped spacers constructed of an electrical insulating material. Both the first and second contacts are connected to an oscillator having a frequency dependent upon the capacitance of the capacitor. The capacitance of the capacitor varies in an amount proportional to the amount of air contained within the dielectric fluid to thereby vary the frequency of the oscillator. The frequency output from the oscillator is connected to an indicator circuit to provide an indication of the oscillator frequency and thus of the amount of air within the dielectric fluid.

We claim: 
     
       1. A device for detecting the presence of air in a fluid system containing a dielectric fluid, comprising: a capacitor comprising a first electrical plate comprising a tube, a second electrical plate comprising a rod, and means for coaxially mounting said rod in said tube, said plates being spaced apart from each other and defining a continuous cylindrical chamber therebetween;   means for fluidly connecting said chamber to said fluid system; and   means for determining the capacitance of said capacitor, comprising an oscillator, said oscillator including said capacitor as an element so that a variation of the capacitance of said capacitor varies the frequency of said oscillator,   wherein said mounting means comprises a pair of discs, each disc constructed of an electrically insulating material and having an axial hole and a further hole spaced from said axial hole, said discs being positioned within said tube so that an outer periphery of each disc engages an inner periphery of said tube at axially spaced positions and said rod being positioned in said discs' axial holes.   
     
     
       2. The invention according to claim 1, wherein said tube comprises a shoulder, and wherein one of said disks is abuttable against said shoulder. 
     
     
       3. The invention according to claim 1, wherein said tube is capped by an end cap, and wherein said device additionally comprises an annular spacer disposed between and abutting said end cap and one of said disks. 
     
     
       4. The invention as defined in claim 1 wherein said rod includes a reduced diameter portion at each end.